If you had to subtract 426 from 913, how many times would you need to regroup? how can you tell?

Regrouping in subtraction means that if you can't subtract because the digit on the bottom has a greater value than the digit on the top (such as 3-6)m so in this case you would have to regroup twice.

Ithink it can be put them in order by 4 possible ways.that mean 3 group of 10 rocks,or an another group of 8 rocks.